It is known to chemically stabilize nanoparticles, particularly pigments for inks, by means of surface modification to prevent aggregate formation and flocculation of the nanoparticles in the ink. Such stabilization is also used for functional inks based on metallic nanoparticles.
Stabilized nanoparticles can be synthesized for example out of gold chloride (AuCl3) via the Brust-Schiffrin synthesis in a 2-phase system (Brust et al. Synthesis of Thiol-derivatised Gold Nanoparticles in a Two-phase Liquid-Liquid System. J. CHEM. SOC., CHEM. COMMUN., 1994, p. 801). The method provides stabilized gold particles of 1-3 nm in size. Dodecanthiol was used as a stabilizer molecule.
From U.S. Pat. No. 7,963,646 B2, it is known to produce an aqueous ink from Au or Ag nanoparticles. Water-soluble polymers, particularly carboxymethyl cellulose, were proposed as stabilizer molecules.
From U.S. Pat. No. 8,227,022 B2, it is known to produce metal salts in an aqueous dispersion, particularly for an ink. The production method has a pre-reduction step of the metal salts using a water-soluble polymer and subsequently a complete chemical reduction of the particles.
From WO 2001068596 A1, it is known to use stabilized gold nanoparticles for decorative purposes.
From EP 1 818 123 B1, it is also known to use stabilized gold nanoparticles. The particles are further functionalized.
From DE 10 2012 021 222 A1, an ink-jet printing process is known, in which a nano-porous layer is produced by the subsequent sintering of multiple nanoparticle types.
Nanoparticles for inks are generally absorbed in chemically synthesized solvents and additives. These are generally very toxic and thus not compatible with some production processes. For example, these cannot be used for food packaging.
Another disadvantage is the high melting temperature of the nanoparticles or sintering temperature of the inks based on them.